The D locus: turning colour down
The dilution gene lives at the D locus. D is dominant and allows full pigmentation; d is recessive and dilutes the pigment. Only a d/d dog is actually dilute — a D/d dog looks fully coloured but carries dilution and can pass it on.
In the homozygous recessive form, dilution is thought to work by clumping the pigment granules in the hair shaft, which affects both eumelanin and phaeomelanin. On a black‑based dog the result is blue or slate.
Blue & slate
The nose, eye rims and lips dilute along with the coat, so a blue dog wears a soft grey nose instead of black. Eye colour tends to run pale, from a light amber to a light brown.
Lilac — brown and blue together
Lilac is the prettiest trick in the dilution box: it needs the dog to be both brown and dilute. To produce a lilac puppy, both parents must carry brown and blue.
A lilac’s nose is a rosey‑grey — dilute brown — which distinguishes it from the cleaner grey of a blue dog. Because it stacks two recessives, lilac is comparatively uncommon.
Dilute and merle together
Merle is itself a dilution pattern, so a slate merle is a dilute dog whose merle patches sit on an already‑softened base. Read the nose and the darkest points to name the true colour.
